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The pure rotational spectrum of the CCl+ (X1Σ+) cation has been observed for the first time using a cryogenic ion trap apparatus and applying an action spectroscopy scheme. The major isotopic species 12C35Cl+ was observed up to the J = 4 ← 3 transition around 191 GHz and 12C37Cl+ was observed up to J = 3 ← 2. All transitions exhibit (partially) resolved hyperfine structure from the presence of the chlorine nuclei (both I = 3/2). This study provides the data needed for future sensitive radio astronomical searches for CCl+ in space. [ABSTRACT FROM AUTHOR]

The A˜ [sup 3]Π[sub i]←X˜ [sup 3]Σ[sup -] electronic transition of a carbon-chain molecule CCS has been observed for the first time by laser induced fluorescence spectroscopy. The species was generated with a pulsed discharge of 0.5% C[sub 2]H[sub 2] and 0.5% CS[sub 2] diluted in Ar via a pulsed supersonic jet. A number of bands in the 690-675 nm and 600-615 nm regions (14 500-14 800, 16 200-16 600 cm-1) were observed and assigned to those of CCS using ground state combination differences. Three of the bands in each region were found to belong to the three A˜ [sup 3]Π[sub i] spin-orbit components of the A˜ [sup 3]Π[sub i]←X˜ [sup 3]Σ[sup -] transition (T[sub v]=14 662.777(4) and 16 423 cm-1), and an effective set of rotational constants for the upper states were obtained. The higher energy band was heavily perturbed, preventing the determination of effective constants for this band. These bands have been tentatively assigned as two successive bands in the A˜ [sup 3]Π[sub i](n,0,0) progression with a resultant effective value of 1760 cm-1 for the A˜ [sup 3]Π[sub i] ν[sub 1] vibrational fundamental. Dispersed fluorescence spectra from the A˜ [sup 3]Π[sub i]←X˜ [sup 3]Σ[sup -] band of CCS have also been observed, yielding definitive experimental information on the vibrational structure of the X˜ [sup 3]Σ[sup -] ground state for the first time. The three harmonic frequencies were determined to be 1708.2(40) cm-1, 862.5(19) cm-1, and 269.3(13) cm-1 for ω[sub 1] (CC stretch), ω[sub 2] (CS stretch), and ω[sub 3] (CCS bend), respectively. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of the CCl+ (X1Σ+) cation has been observed for the first time using a cryogenic ion trap apparatus and applying an action spectroscopy scheme. The major isotopic species 12C35Cl+ was observed up to the J = 4 ← 3 transition around 191 GHz and 12C37Cl+ was observed up to J = 3 ← 2. All transitions exhibit (partially) resolved hyperfine structure from the presence of the chlorine nuclei (both I = 3/2). This study provides the data needed for future sensitive radio astronomical searches for CCl+ in space. [ABSTRACT FROM AUTHOR]

We investigated the interlinked N-H and N-C photochemistry of primary and secondary amines via the state-resolved detection of vibrationally excited CH 3 product and H atom product by 200-235 nm dimethylamine photodissociation using resonance-enhanced multiphoton ionization (REMPI) and velocity map imaging (VMI) techniques. The out-of-plane bending (ν 2 ) vibrationally excited CH 3 showed a bimodal translational energy distribution that became unimodal with a near-zero product yield at longer photolysis wavelengths (λ photolysis ). In contrast, a unimodal distribution was observed for the C-H stretching (ν CH ) vibrationally excited CH 3 products with an almost constant product yield in the examined λ photolysis region. We ascribed the state-specific energy releases of the CH 3 products to two reaction pathways based on calculations of the potential energy surface (PES): the direct N-CH 3 dissociation pathway and the indirect N-CH 3 dissociation pathway via the N-H bond conical intersection. Meanwhile, the H atom product showed a bimodal energy distribution similar to the ammonia photodissociation model, with an excited-state counterproduct channel that became accessible at a shorter λ photolysis . These results suggest that the N-H and N-C bond dissociations are connected, and these dissociations cause different photochemistry between primary/secondary amines and tertiary amines.

We investigated the photodissociation dynamics of CpCo(CO) 2 (cyclopentadienylcobalt dicarbonyl) in metal-to-ligand charge transfer (MLCT) bands. By employing DFT calculations, the absorption band (210-240 nm) was characterized as a charge transfer from the Co center to the Cp (cyclopentadienyl, C 5 H 5 ) ligand. Ion imaging was utilized to analyze the CO fragments and coordinatively unsaturated complexes (CpCoCO, CpCo, and CoC 3 H 3 ) across the entire MLCT band. Measuring the production yields of individual unsaturated complexes as a function of photolysis wavelength by considering wavelength dependence indicated the involvement of several photochemical pathways: the first photodissociation and sequential dissociation of CpCo(CO) 2 , and the second photodissociation of unsaturated intermediates within the pulse duration of the photolysis laser. The recoil velocity shifts of CpCo and CoC 3 H 3 were attributed to the onset of the sequential dissociation of CpCoCO. Evidence for the second photodissociation of CpCoCO was obtained through the matching of linear momenta between the CO( v = 0, 1) and CpCo fragments. The DFT calculations performed to determine the electronic structures and potential energy curves for photoinduced CO loss in CpCo(CO) 2 and CpCoCO supported our interpretation of the experimental results. This study presents a practical approach to selectively detecting specific processes among the mixture of products and intermediates when photolyzing transition-metal carbonyls, as their concurrent generation is unavoidable in laser-based experiments.

The internal energy distributions of reaction products are important information in clarifying the mechanism of chemical reactions. There are few reports of the nascent vibrational energy distribution of CS(X 1 Σ + ) generated in the S( 1 D) + CS 2 reaction. As long as S( 1 D) is produced by photodissociation of CS 2 , CS(X 1 Σ + ), as a product of the chemical reaction and as a photoproduct of CS 2 is indistinguishable. In this study, S( 1 D) was generated by the photolysis of OCS at 248 nm, where CS 2 hardly dissociates, and CS(X 1 Σ + ) was generated only by the S( 1 D) + CS 2 reaction. The vibrational levels v ″ = 0-6 of CS(X 1 Σ + ) were detected with laser-induced fluorescence (LIF) via the A 1 Π-X 1 Σ + transition. The identical time profiles of the LIF intensities showed that all the vibrational levels were produced by the S( 1 D) + CS 2 reaction. The relative nascent vibrational populations of CS(X 1 Σ + ) determined from the area intensities of the excitation spectra are 1.00 ± 0.11/0.58 ± 0.06/0.31 ± 0.03/0.078 ± 0.009/0.013 ± 0.001/<0.002/<0.002 (the values for v ″ = 5 and 6 are the upper limits) for v ″ = 0/1/2/3/4/5/6. The distribution agrees well with the statistical (prior) distribution.

Ultraviolet photochemistry of iron pentacarbonyl, Fe(CO) 5 , was investigated with resonantly enhanced multiphoton ionization (REMPI) spectroscopy and ion imaging. The REMPI spectrum of CO photofragments, generated by ultraviolet irradiation of Fe(CO) 5 , showed the generation in the highly vibrationally excited states with v = 11-15. Analysis of the band intensities observed in the 213-235 nm region indicated that the high- v CO generation was maximized at around 220 nm. Generation yields of the coordinatively unsaturated intermediates, Fe(CO) n =1-4 , were measured as a function of the photolysis wavelength using a nonresonant detection scheme. The yield spectrum of FeCO was correlated with that of the high- v CO fragments, suggesting high- v CO generation in the photodissociation of FeCO. The density functional theory calculations of the excited states of FeCO showed an intense photoabsorption to the metal-centered state near 220 nm. The theoretical results were consistent with the interpretation of FeCO + h ν → Fe + high- v CO, which was experimentally indicated. The momentum distribution obtained from the velocity distributions of Fe, Fe(CO) 4 , and CO fragments further supported that Fe is the counter-product of the high- v CO fragment. The present results provided selective observation of the photochemistry of the unsaturated iron carbonyl complexes, which has not been well elucidated in laser-based experiments because of the uncontrollable sequential photodissociation producing mixed Fe(CO) n intermediates.

The photodissociation dynamics of the heteroleptic Co(CO) 3 NO complex were investigated in the metal-to-carbonyl (CO) ligand charge-transfer band to compare the reactivity of the CO and nitrosyl (NO) ligands. The final state distributions of both the CO and NO fragments were measured using resonance-enhanced multiphoton ionization (REMPI) spectroscopy and velocity-map ion-imaging. The primary CO photofragment was differentiated from the secondary fragments of the subsequent unimolecular decomposition of coordinatively unsaturated intermediates by comparing the momentum distributions. The internal energy of the Co(CO) 2 NO intermediate was sufficiently high (≥348 kJ/mol) to be generated in the electronic excited state, indicating the occurrence of the primary CO elimination on an excited state. The NO fragments exhibited two velocity components. The analysis of the final state distributions suggested that the higher- and lower-kinetic-energy components originated from the direct primary elimination and sequential elimination, respectively. The direct photoelimination through a transiently bent ligand conformation was illustrated on the basis of a two-dimensional REMPI approach and time-dependent density functional theory calculations. The present results of both ligands demonstrate the correlation between elimination mechanisms and possible ligand conformations in the electronic excited state.

Using two different action spectroscopic techniques, a high-resolution quantum cascade laser operating around 1300 cm-1 and a cryogenic ion trap machine, the proton shuttle motion of the cations HHe2+ and HHe3+ has been probed at a nominal temperature of 4 K. For HHe3+, the loosely bound character of this complex allowed predissociation spectroscopy to be used, and the observed broad features point to a lifetime of a few ps in the vibrationally excited state. For He-H+-He, a fundamental linear molecule consisting of only three nuclei and four electrons, the method of laser-induced inhibition of complex growth (LIICG) enabled the measurement of three accurate rovibrational transitions, pinning down its molecular parameters for the first time.

The title compound, 2-ethylhexyl-4-methoxycinnamate (2EH4MC), is known as a typical ingredient of sunscreen cosmetics that effectively converts the absorbed UV-B light to thermal energy. This energy conversion process includes the nonradiative decay (NRD): trans - cis isomerization and finally going back to the original structure with a release of thermal energy. In this study, we performed UV spectroscopy for jet-cooled 2EH4MC to investigate the electronic/geometrical structures as well as the NRD mechanism. Laser-induced-fluorescence (LIF) spectroscopy gave the well-resolved vibronic structure of the S 1 -S 0 transition; UV-UV hole-burning (HB) spectroscopy and density functional theory (DFT) calculations revealed the presence of syn and anti isomers, where the methoxy (-OCH 3 ) groups orient in opposite directions to each other. Picosecond UV-UV pump-probe spectroscopy revealed the NRD process from the excited singlet (S 1 ( 1 ππ*)) state occurs at a rate constant of ∼10 10 -10 11 s -1 , attributed to internal conversion (IC) to the 1 nπ* state. Nanosecond UV-deep UV (DUV) pump-probe spectroscopy identified a transient triplet (T 1 ( 3 ππ*)) state, whose energy (from S 0 ) and lifetime are 18 400 cm -1 and 20 ns, respectively. These results demonstrate that the photoisomerization of 2EH4MC includes multistep internal conversions and intersystem crossings, described as "S 1 ( trans , 1 ππ*) → 1 nπ* → T 1 ( 3 ππ*) → S 0 ( cis )".

The electronic states and photochemistry including nonradiative decay (NRD) and trans(E) → cis(Z) isomerization of methylcinnamate (MC) and its hydrogen-bonded complex with methanol have been investigated under jet-cooled conditions. S1(1nπ*) and S2(1ππ*) are directly observed in MC. This is the first direct observation of S1(1nπ*) in cinnamate derivatives. Surprisingly, the order of the energies between the nπ* and ππ* states is opposite to substituted cinnamates. TD-DFT and SAC-CI calculations support the observed result and show that the substitution to the benzene ring largely lowers the 1ππ* energy while the effect on 1nπ* is rather small. The S2(ππ*) state lifetime of MC is determined to be equal to or shorter than 10 ps, and the production of the transient T1 state is observed. The T1(ππ*) state is calculated to have a structure in which propenyl C[double bond, length as m-dash]C is twisted by 90°, suggesting the trans → cis isomerization proceeds via T1. The production of the cis isomer is confirmed by low-temperature matrix-isolated FTIR spectroscopy. The effect of H-bonding is examined for the MC-methanol complex. The S2 lifetime of MC-methanol is determined to be 180 ps, indicating that the H-bonding to the C[double bond, length as m-dash]O group largely prohibits the 1ππ* → 1nπ* internal conversion. This lifetime elongation in the methanol complex also describes well a higher fluorescence quantum yield of MC in methanol solution than in cyclohexane, while such a solvent dependence is not observed in para-substituted MC. Determination of the photochemical reaction pathways of MC and MC-methanol will help us to design photofunctional cinnamate derivatives.

The ground state of He-HCO+ is investigated using a recently developed double resonance technique, consisting of a rotational transition followed by a vibrational transition into a dissociative state. In order to derive precise predictions for the rotational states, the high resolution infrared predissociation spectroscopy of the v1 C-H stretching mode is revisited. Eleven pure rotational transitions are measured via the double resonance method. A least squares fit of these transitions to a standard linear rotor Hamiltonian reveals that the semirigid rotor model cannot fully describe the loosely bound He-HCO+ complex. The novel double resonance technique is compared with other action spectroscopic schemes, and some potential future applications are presented.

A novel rotational spectroscopy method applicable to ions stored in cold traps is presented. In a double resonance scheme, rotational excitation is followed by vibrational excitation into a dissociative resonance. Its general applicability is demonstrated for the CH&#95;{3}^{+}-He complex, which undergoes predissociation through its C-H stretching modes ν&#95;{1} and ν&#95;{3}. High resolution rotational transitions are recorded for this symmetric top, and small unexpected splittings are resolved for K=1. Advantages and potential future applications of this new approach are discussed.

An experimental and theoretical study has been carried out to elucidate the nonradiative decay (NRD) and trans(E) → cis(Z) isomerization from the S1 (1ππ*) state of structural isomers of hydroxy methylcinnamate (HMC); ortho-, meta- and para-HMC (o-, m- and p-HMC). A low temperature matrix-isolation Fourier Transform Infrared (FTIR) spectroscopic study revealed that all the HMCs are cis-isomerized upon UV irradiation. A variety of laser spectroscopic methods have been utilized for jet-cooled gas phase molecules to investigate the vibronic structure and lifetimes of the S1 state, and to detect the transient state appearing in the NRD process. In p-HMC, the zero-point level of the S1 state decays as quickly as 9 ps. A transient electronic state reported by Tan et al. (Faraday Discuss. 2013, 163, 321-340) was reinvestigated by nanosecond UV-tunable deep UV pump-probe spectroscopy and was assigned to the T1 state. For m- and o-HMC, the lifetime at the zero-point energy level of S1 is 10 ns and 6 ns, respectively, but it becomes substantially shorter at an excess energy higher than 1000 cm-1 and 600 cm-1, respectively, indicating the onset of NRD. Different from p-HMC, no transient state (T1) was observed in m- nor o-HMC. These experimental results are interpreted with the aid of TDDFT calculations by considering the excited-state reaction pathways and the radiative/nonradiative rate constants. It is concluded that in p-HMC, the trans → cis isomerization proceeds via a [trans-S1 → 1nπ* → T1 → cis-S0] scheme. On the other hand, in o- and m-HMC, the isomerization proceeds via a [trans-S1 → twisting along the C[double bond, length as m-dash]C double bond by 90° on S1 → cis-S0] scheme. The calculated barrier height along the twisting coordinate agrees well with the observed onset of the NRD channel for both o- and m-HMC.

The protonated oxygen molecule, O 2 H + , and its helium complex, He-O 2 H + , have been investigated by vibrational action spectroscopy in a cryogenic 22-pole ion trap. For the He-O 2 H + complex, the frequencies of three vibrational bands have been determined by predissociation spectroscopy. The elusive O 2 H + has been characterized for the first time by high-resolution rovibrational spectroscopy via its ν 1 OH-stretching band. Thirty-eight rovibrational fine structure transitions with partly resolved hyperfine satellites were measured (56 resolved lines in total). Spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a triplet electronic ground state, X̃ 3 A '' , yielding a band origin at 3016.73 cm -1 . Based on these spectroscopic parameters, the rotational spectrum is predicted, but not yet detected.

Highly vibrationally excited disulfur S 2 in the X 3 Σ g - and a 1 Δ g states has been detected in the gaseous mixture of O 3 and OCS irradiated with light at 266 nm. Generation of CO 2 in the reaction system has been reported; however, no direct detection of sulfur atoms (S( 3 P) and S( 1 D)) has been made. In the present study, we have employed the two-photon laser-induced fluorescence (2P-LIF) technique to detect S( 3 P) and S( 1 D) directly and recorded the time profiles of the atoms at varying pressures of OCS. Kinetic analyses of the profiles show that (i) S( 1 D) is generated in the O( 1 D) + OCS reaction and consumed by the S( 1 D) + OCS reaction, and (ii) S( 3 P) is mainly generated in the O( 1 D) + OCS reaction instead of quenching of S( 1 D) by collisions with OCS and ambient gases. The vibrational levels v = 19 and 10 of the respective electronic states X 3 Σ g - and a 1 Δ g of S 2 were detected in the O 3 /OCS/266 nm system. The two vibrational levels cannot be generated by the available energy of the S( 3 P) + OCS reaction, giving evidence that S 2 in the X 3 Σ g - and a 1 Δ g states are generated by the S( 1 D) + OCS reaction.

The primary photochemical reaction of nitromethane (NM) after ππ* excitation is known to be C-N bond cleavage (CH 3 NO 2 + hν → CH 3 + NO 2 ). On the other hand, NO 2 can be formed in both the ground and excited states, and identification of the electronic state of the NO 2 product has been a central subject in the experimental and theoretical studies. Here we present time-resolved photoelectron spectroscopy using vacuum-ultraviolet probe pulses to observe all transient electronic states of NM and the reaction products. The result indicates that ultrafast internal conversion occurs down to S 1 and S 0 within 24 fs, and the dissociation proceeds on the S 1 surface (τ diss ≲ 50 fs), leading to comparable product yields of NO 2 (A) and NO 2 (X). The overall dissociation quantum yield within our observation time window (<2 ps) is estimated to be 0.29.

Ion-imaging and dispersed fluorescence spectroscopy are employed for the photodissociation dynamics study of methylamine in the photolysis wavelength range 205-213 nm. The methyl radical product is found to populate a wide range of ro-vibrational states, among which the CH 3 fragment generated in the v = 0 state shows a bimodal kinetic energy distribution. The internal energy analysis of the NH 2 counterproduct indicates that a lower kinetic energy component, which was observed only with the CH 3 (v=0) fragment, energetically matches the electronically excited à 2 A 1 state. The dispersed fluorescence spectrum, whose band structure is assigned to the à 2 A 1 → X̃ 2 B 1 transition, provides evidence of the CH 3 (v=0) + NH 2 (à 2 A 1 ) pathway. The branching mechanism of the product pathway is discussed in terms of nuclear dynamics in the long-range region, where the conical intersection between the excited- and ground-state potential energy surfaces can play a significant role.

The nonradiative decay pathways of jet-cooled para-methoxy methylcinnamate (p-MMC) and para-methoxy ethylcinnamate (p-MEC) have been investigated by picosecond pump-probe and nanosecond UV-Deep UV pump-probe spectroscopy. The possible relaxation pathways were calculated by the (time-dependent) density functional theory. We found that p-MMC and p-MEC at low excess energy undergo multistep intersystem crossing (ISC) from the bright S 1 ( 1 ππ*) state to the lowest triplet T 1 ( 3 ππ*) state via two competing pathways through the T 2 state in the time scale of 100 ps: (a) stepwise ISC followed after the internal conversion (IC) from S 1 to the dark 1 nπ* state; (b) direct ISC from the S 1 to T 2 states. These picosecond multistep ISCs result in the torsion of C═C double bond by ∼95° in the T 1 state, whose measured adiabatic energy and lifetime are 16577 cm -1 and ∼20 ns, respectively, for p-MMC. These results suggest that the ISC processes play an indispensable role in the photoprotecting sunscreens in natural plants.

In this paper, we present a photodissociation dynamics study of nitromethane at 213 nm in the π → π(*) transition. Resonantly enhanced multiphoton ionization spectroscopy and ion-imaging were applied to measure the internal state distributions and state-resolved scattering distributions of the CH3, NO(X (2)Π, A (2)Σ(+)), and O((3)PJ) photofragments. The rotationally state-resolved scattering distribution of the CH3 fragment showed two velocity components, of which the slower one decreased the relative intensity as the rotational and vibrational excitations. The translational energy distribution of the faster CH3 fragment indicated the production of the NO2 counter-product in the electronic excited state, wherein 1 (2)B2 was the most probable. The NO(v = 0) fragment exhibited a bimodal translational energy distribution, whereas the NO(v = 1 and 2) fragment exhibited a single translational energy component with a relatively larger internal energy. The translational energy of a portion of the O((3)PJ) photofragment was found to be higher than the one-photon dissociation threshold, indicating the two-photon process involved. The NO(A (2)Σ(+)) fragment, which was detected by ionization spectroscopy via the Rydberg ← A (2)Σ(+) transition, also required two-photon energy. These experimental data corroborate the existence of competing photodissociation product pathways, CH3 + NO2,CH3 + NO + O,CH3O + NO, and CH3NO + O, following the π → π(*) transition. The origins of the observed photofragments are discussed in this report along with recent theoretical studies and previous dynamics experiments performed at 193 nm.

The reaction of electronically excited sulfur S((1)D) with OCS has exothermic channels generating S(2) in two electronic states X(3)Σ(g)– and a(1)Δ(g). The a(1)Δ(g) state is correlated directly to the reactants via the spin-allowed singlet surface; the X(3)Σ(g)– state, on the other hand, is a product of the spin-forbidden channel. There has been no report on kinetic evidence for the simultaneous generation of the two electronic states, although the two electronic states have been detected so far. The previous studies showed that little energy was released into rotation or vibration of the S(2) products despite large heats of reactions (228 and 175 kJ mol(-1) for generation of X(3)Σ(g)– and a(1)Δ(g), respectively). In the present study, S((1)D) was generated by the photolysis of OCS at 248 nm in a buffer He at 298 K, and the resulting two electronic states of S(2) (X(3)Σ(g)– and a(1)Δ(g)) were detected with dispersed laser-induced fluorescence (LIF) via the B(3)Σ(u)(-)–X(3)Σ(g)– and f(1)Δ(u)-a(1)Δ(g) transitions, respectively. Not only excitation but also dispersed fluorescence spectra made it possible to find a single rotational line of the vibrational level of interest. The time-resolved LIF intensities of the initial growth of the X(3)Σ(g)– and a(1)Δ(g) states showed identical OCS pressure dependences, giving the overall rate coefficient of the S(1D) + OCS reaction to be [3.2 ± 0.2(2σ)] × 10(-10) cm3 molecule(-1) s(-1). The simultaneous generation of the two electronic states indicates that the intersystem crossing plays a role in opening the spin-forbidden channel. As for the reaction dynamics, vibrational levels up to v = 19 of X(3)Σ(g)– and 11 of a(1)Δ(g) have been detected, which is distinctly different from the previous studies. The reaction mechanism has been discussed on the basis of the potential energies reported so far.

The ultraviolet photodissociation dynamics of allyl iodide (C3H5I) have been studied by ion-imaging at 266 nm and 213 nm. These photolysis wavelengths are located in the two lowest absorption bands in the near-ultraviolet region. The atomic iodine products were detected by [2+1] resonantly enhanced multiphoton ionization spectroscopy. The spectra showed that the branching fraction for the spin-orbit excited ((2)P(1/2)) state was larger than that for the ground ((2)P(3/2)) state at both photolysis wavelengths. The state-resolved scattering images of iodine showed two maxima in the velocity distributions in the (2)P(3/2) state and a single peak in the (2)P(1/2) state. The spin-orbit specificity indicates that the C-I bond cleavage at both absorption bands is governed by the dissociative n(I)σ*(C-I) potential energy surfaces. The nascent internal energy distribution of the allyl radical (C3H5) counter product, which was obtained by the analysis of the state-resolved scattering distributions, showed a marked difference between the photolysis at 266 nm and 213 nm. The generation of the colder C3H5 with the higher translational energy at 266 nm implied the direct photoexcitation to the n(I)σ*(C-I) repulsive surfaces, whereas the internally hot C3H5 at 213 nm was ascribed to the local π(CC)π*(CC) photoinitiation in the allyl framework followed by predissociation to the n(I)σ*(C-I) states.

Pure rotational transitions of the Ar-CS van der Waals complex have been observed by Fourier Transform Microwave (FTMW) and FTMW-millimeter wave double resonance spectroscopy. Rotational transitions of v(s) = 0, 1, and 2 were able to be observed for normal CS, together with those of C(34)S in v(s) = 0, where vs stands for the quantum number of the CS stretching vibration. The observed transition frequencies were analyzed by a free rotor model Hamiltonian, where rovibrational energies were calculated as dynamical motions of the three nuclei on a three-dimensional potential energy surface, expressed by analytical functions with 57 parameters. Initial values for the potential parameters were obtained by high-level ab initio calculations. Fifteen parameters were adjusted among the 57 parameters to reproduce all the observed transition frequencies with the standard deviation of the fit to be 0.028 MHz.

The scattering distributions of state-selected CH3 products are measured for the O((1)D2) reaction with CH4 using a crossed molecular beam ion imaging method at collision energies of 0.9-6.8 kcal mol(-1). The results are compared with the reaction with CD4 to examine the isotope effects. The scattering distributions exhibit contributions from both the insertion and abstraction pathways, respectively, on the ground- and excited-state potential energy surfaces. Insertion is the main pathway, and it provides a strongly forward-enhanced angular distribution of methyl radicals. Abstraction is a minor pathway, causing backward scattering of methyl radicals with a discrete speed distribution. From the collision energy dependence of the abstraction/insertion ratio, the barrier height for the abstraction pathway is estimated to be 0.7 ± 0.3 and 0.8 ± 0.1 kcal mol(-1) for O((1)D2) with CH4 and CD4, respectively. The insertion pathway of the O((1)D2) reaction with CH4 has a narrower angular width in the forward scattering and a larger insertion/abstraction ratio than the reaction with CD4, which indicates that the insertion reaction with CH4 has a larger cross section and a shorter reaction time than the reaction with CD4. Additionally, while the insertion reaction with CD4 exhibits strong angular dependence of the CD3 speed distribution, CH3 exhibits considerably smaller dependence. The result suggests that, although intramolecular vibrational redistribution (IVR) within the lifetime of the methanol intermediate is restrictive in both isotopomers, relatively more extensive IVR occurs in CD3OD than CH3OH, presumably due to the higher vibrational state density.

The Ã(3)A"-X̃(3)Σ(-) electronic transition of the HCCN∕DCCN radical was observed by laser-induced fluorescence spectroscopy. Rotationally resolved excitation spectra were observed for HCCN and DCCN, and effective molecular constants of the upper state were determined. The observed intensities of the rotational lines were anomalous, probably due to a level-dependent non-radiative decay process in the excited state. Fluorescence depletion spectroscopy was applied in order to observe non-fluorescent vibronic levels. A dispersed fluorescence spectrum was also observed to determine the vibrational level structure in the ground electronic state. The observed vibrational structures in the fluorescence depletion and dispersed fluorescence spectra were tentatively assigned based on the results of ab initio calculations.

The vibrational relaxation of OH(X(2)Π) by collisions with rare gases is very slow due to small molecular interactions. No measurement of the rate coefficients has been made for relaxation of relatively low vibrational levels v ≤ 4 of OH by He, and there is only one report of the upper limit for v = 2, <1 × 10(-14) cm(3) molecule(-1) s(-1). In this article, we have studied vibrational relaxation of the levels v = 1-4 of OH(X(2)Π) by collisions with He. A gaseous mixture of O3 and H2 in a carrier gas at 70-130 Torr of He was irradiated at 266 nm, and OH(X(2)Π, v ≤ 4) was generated in the reaction O((1)D) + H2. A single vibrational level of OH was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π transition. Time-resolved LIF intensities of OH(v) were recorded, and kinetic analysis was made by an originally developed integrated profiles method (IPM). On the basis of the evaluation of the pressure-dependent rate coefficients of diffusion loss and the effect of impurities on the kinetics, the rate coefficients of vibrational relaxation for OH(X(2)Π, v = 1-4) by He have been determined to be (2.9 ± 1.5) × 10(-17), (1.4 ± 0.4) × 10(-16), (5.2 ± 0.5) × 10(-16), and (1.6 ± 0.2) × 10(-15) cm(3) molecule(-1) s(-1) for v = 1, 2, 3, and 4, respectively (the confidence limits are 2σ). The rate coefficients are larger at higher vibrational levels and smoothly correlate to those reported previously for v = 10-12.

The linear kinetic analysis called the integrated profiles method (IPM) makes it simple to analyze the multistep relaxation processes of vibrational manifold. The problem that plots for linear regression in the IPM analysis cannot be made, however, has been found in the study of self relaxation of O2(X3Σ(-)g, v = 6-8). The cause of the problem is the identical time-dependence of the populations of the adjacent vibrational levels. An addition of CF4 into the system made a difference in the time profiles and enabled us to make IPM analysis and determine the rate coefficients. In the experiments, a gaseous mixture of O3/O2/CF4 in an Ar carrier at 298 K was irradiated at 266 nm, and the direct photoproduct O2(X3Σ(-)g, v = 6-9) from O3 was detected by laser-induced fluorescence (LIF)in the B3Σu-X3Σ(-)g transition. Time-resolved LIF intensities of O2(X3Σ(-)g, v) at various pressures of O2 and fixed pressure of CF4 were recorded. The resulting rate coefficients for v = 6−8 correlate smoothly with those for v ≤ 5 and v ≥ 8 reported previously.The vibrational-level dependence (v = 2-13) of the rate coefficients for relaxation of O2(X3Σ(-)g, v) by O2 is accounted for by the balance between the harmonic transition probabilities and the energy defect in the V-V energy-transfer mechanism.

The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO.

The rovibrational state distributions and state-resolved scattering distributions of CD(3) radicals produced by the reaction O((1)D) + CD(4) were investigated by crossed molecular beam ion imaging. The rotational structure of the resonance-enhanced multiphoton ionization spectrum of CD(3) in the ground vibrational state indicates that the low K rotational states of CD(3) radicals are preferentially populated. The state-resolved scattering distributions of CD(3) (v = 0) and those of the excited states of the out-of-plane bending (v(2)) mode exhibit a structureless forward-scattering component due to an insertion pathway and a structured backward-scattering component due to an abstraction path. The scattering distributions of CD(3) in the excited state of the C-D symmetric stretch (v(1)) do not exhibit the abstraction component. The scattering distribution of the abstraction component gradually extends in the forward direction with increasing intensity as the v(2) vibration becomes more strongly excited. This suggests that abstraction with a larger impact parameter results in stronger excitation of v(2).

We performed He I ultraviolet photoelectron spectroscopy (UPS) of jet-cooled aromatic molecules using a newly developed photoelectron imaging (PEI) spectrometer. The PEI spectrometer can measure photoelectron spectra and photoelectron angular distributions at a considerably higher efficiency than a conventional spectrometer that uses a hemispherical energy analyzer. One technical problem with PEI is its relatively high susceptibility to background electrons generated by scattered He I radiation. To reduce this problem, we designed a new electrostatic lens that intercepts background photoelectrons emitted from the repeller plate toward the imaging detector. An energy resolution (ΔE/E) of 0.735% at E = 5.461 eV is demonstrated with He I radiation. The energy resolution is limited by the size of the ionization region. Trajectory calculations indicate that the system is capable of achieving an energy resolution of 0.04% with a laser if the imaging resolution is not limited. Experimental results are presented for jet-cooled benzene and pyridine, and they are compared with results in the literature.

The vibrational levels of O2(X3Sigma(g)-) generated in the ultraviolet photolysis of O3 at 266 nm were detected via laser-induced fluorescence (LIF) of the B3Sigma(u)- - X3Sigma(g)- system. The nascent vibrational energy distributions of O2(X3Sigma(g)-, nu = 6-13) have been measured by two different methods. One is a kinetic analysis based on the originally developed integrated profiles method (IPM). The time-resolved LIF of a single vibrational level has been recorded in the presence of CF4 or O2 as a relaxation partner. The IPM analysis of the profiles gave the relative detectabilities of adjacent vibrational levels, and the initial relative populations of the vibrational levels have been determined from the intensities of LIF subsequent to the photolysis. The other is the analysis of the area intensities of the LIF of the vibrational levels of interest. The rotational levels with the identical quantum numbers of different vibrational levels in the X3Sigma(g)- state were excited to a common vibrational level nu' = 0 in the B3Sigma(u)- state. Correction for the LIF intensities with the Franck-Condon factors was made, and the initial relative populations have been obtained. The two different methods have given similar nascent vibrational energy distributions, and comparison to the previous reports has been made.

We have constructed a photoelectron imaging spectrometer with super-resolution image processing and have applied it to the photoionization of nitric oxide and benzene in molecular beams. A field programmable gate array is employed for real-time subpixel centroiding calculations on hardware, providing 64 megapixel resolution (8192 x 8192 pixels). We examined eight different centroiding algorithms based on the center-of-gravity (COG) and Gaussian fitting (Gauss) methods and have found that the two-dimensional COG (2D-COG) and weighted mean of Gaussian center (w-Gauss) methods have the best performance. The excellent performance of the instrument is demonstrated by visualizing a 25 mum diameter pore structure of an MCP, indicating a spatial resolution of 0.03%. The photoelectron image in one-color (1 + 1) resonance-enhanced multiphoton ionization of nitric oxide using a nanosecond laser provided a photoelectron kinetic energy resolution of 0.2%. This resolution is currently restricted by charged-particle optics. The photoelectron energy and angular distributions in the one-color (1 + 1) resonance-enhanced multiphoton ionization of benzene via 6(1) and 6(1)1(1) vibronic levels in the S(1) state are also presented. The results demonstrate that photoelectron angular anisotropy varies with the photoelectron kinetic energy and the vibronic state of the cation.

The scattering distributions of rotationally state-selected CD3 products in the O(1D2) reaction with deuterated methane at a collision energy of 5.6 kcal/mol were investigated. Markedly different features were found between the forward and backward scatterings of rovibrationally unexcited CD3, which provides the experimental evidence of the dual reaction mechanisms, i.e., insertion and abstraction on the ground- and excited-state potential energy surfaces, respectively, in this benchmark system. The gradual emergence of forward-backward symmetry in the angular distributions of CD3 in higher rotational states suggests that osculating complexes create rotationally hotter CD3.

A wide range of vibrational levels of O2(X(3)Sigma(g)(-), v = 6-13) generated in the ultraviolet photolysis of O3 was selectively detected by the laser-induced fluorescence (LIF) technique. The time-resolved LIF-excited B(3)Sigma(u)(-)-X(3)Sigma(g)(-) system in the presence of CF4 has been recorded and analyzed by the integrated profiles method (IPM). The IPM permitted us to determine the rate coefficients k(v)(CF4) for vibrational relaxation of O2(X(3)Sigma(g)(-), v = 6-12) by collisions with CF4. Energy transfer from O2 (v = 6-12) to CF4 is surprisingly efficient compared to that of other polyatomic relaxation partners studied so far. The k(v)(CF4) increases with vibrational quantum number v from [1.5 +/- 0.2(2sigma)] x 10(-12) for v = 6 to [7.3 +/- 1.5(2sigma)] x 10(-11) for v = 12, indicating that the infrared-active nu3 vibrational mode of CF4 mainly governs the energy transfer with O2(X(3)Sigma(g)(-), v = 6-12). The correlation between the rate coefficients and fundamental infrared intensities has been discussed based on a comparison of the efficiency of energy transfer by several collision partners.

The dynamics of the O(1D) + HCl --> OH + Cl(2P) reaction are investigated by a crossed molecular beam ion-imaging method and quasiclassical trajectory calculations on the three ab initio potential energy surfaces, the ground 1(1)A' and two excited (1(1)A'' and 2(1)A') states. The scattering experiment was carried out at collision energies of 4.2, 4.5, and 6.4 kcal/mol. The observed doubly differential cross sections (DCSs) for the Cl(2P) product exhibit almost no collision energy dependence over this inspected energy range. The nearly forward-backward symmetric DCS indicates that the reaction proceeds predominantly on the ground-state potential energy surface at these energies. Variation of the forward-backward asymmetry with collision energy is interpreted using an osculating complex model. Although the potential energy surfaces obtained by CASSCF-MRCI ab initio calculations exhibit relatively low potential barriers of 1.6 and 6.5 kcal/mol for 1(1)A'' and 2(1)A', respectively, the dynamics calculations indicate that contributions of these excited states are small at the collision energies lower than 15.0 kcal/mol. Theoretical DCSs calculated for the ground-state reaction pathway agree well with the observed ones. These experimental and theoretical results suggest that the titled reaction at collision energies less than 6.5 kcal/mol is predominantly via the ground electronic state.

The photodissociation dynamics of N2O in the wavelength region of 203-205 nm was studied by velocity map ion imaging. A speed resolution of 0.8% was obtained using standard projection imaging and subpixel centroiding calculations. To investigate N2O dissociation starting from the excited bending levels in the ground electronic state, a supersonic molecular beam and an effusive beam were used. The photoabsorption transition probability from the first excited bending level in the wavelength region of 203-205 nm was estimated to be seven times greater than that from the ground vibrational level.

A crossed molecular beam study is presented for the O((1)D(2))+HCl-->OH+Cl((2)P(J)) reaction at the collision energy of 6 kcal mol(-1). State-resolved doubly differential cross sections are obtained for the Cl((2)P(J=3/2) ) and Cl*((2)P(J=1/2) ) products by velocity-map ion imaging. Both products are slightly more forward scattered, which suggests a reaction mechanism without a long-lived intermediate in the ground electronic state. A small fraction (23 %) of the energy release into the translational degree of freedom indicates strong internal excitation of the counterpart OH radical. The contribution of the electronic excited states of O--HCl to the overall reaction is also examined from the doubly differential cross sections.

State-resolved differential cross sections (DCSs) for the inelastic scattering of NO(j" = 0.5, Omega" = 1/2) + Ar --> NO(j', Omega' = 1/2, 3/2) + Ar were obtained at a collision energy of 516 cm(-1), both experimentally and theoretically. A crossed molecular beam ion-imaging apparatus was used to measure DCSs for 20 final (j', Omega') states, including spin-orbit conserving (DeltaOmega = 0) and changing (DeltaOmega = 1) transitions. Quantum close-coupling scattering calculations on ab initio coupled-cluster CCSD(T) and CEPA (correlated electron pair approximation) potential energy surfaces were also performed. Although small discrepancies were found for the DeltaOmega = 1 transitions, we find marked agreement between theory and experiment for the collision dynamics of this system, which is the paradigm for the collisional relaxation of a molecular radical.

Rotational wave packet revivals on an excited electronic state have been measured by femtosecond time-resolved photoelectron imaging for the first time. The first full revival at 82 ps of S1 (n,pi*) pyrazine was clearly observed in the time dependencies of the photoelectron intensity and the photoelectron angular distribution (PAD). The PAD, measured for laser aligned pyrazine, clearly reflects the different characters of pi* and 3s molecular orbitals.

We evaluated the vascular volume distribution with fine resolution (0.1-1.3 mg myocardial tissue) in the sagittal plane of the left ventricle by using the microsphere filling method in 21 dogs. The coronary arterial volume density in the sagittal plane did not exhibit normal distribution and was characterized by variability among the outer-to-inner layers and within the layers (+2SD/-2SD > 80 times), and the median values in the layers ranged from 4.7 to 22. 9 nl/mg myocardial tissue. The fractal analysis of vascular volume revealed a self-similar nature with a fractal dimension (D value) similar to that of flow distribution (1.20 +/- 0.05 and 1.24 +/- 0. 09 for vascular volume and flow distribution, respectively) and had a more marked variability than the flow. The correlation of the regional vascular volume between adjacent regions decreased as the distance increased. However, the correlation coefficients in the endocardial-to-epicardial direction were significantly higher than those in the anterior-to-posterior direction (P < 0.05 by paired t-test). In conclusion, we determined intramyocardial vascular volume density in the sagittal plane, and the distribution revealed considerable variability, self-similarity, and asymmetry in the correlation among the adjacent regions. These observations could be related to the characteristics of the intramural coronary vascular network.